From: Stephan Szabo <sszabo@megazone.bigpanda.com>
To: Lane Van Ingen <lvaningen@esncc.com>
Cc: pgsql-sql@postgresql.org
Subject: Re: Why Doesn't SQL This Expression Work?
Date: Mon, 22 Aug 2005 13:29:05 -0700 (PDT)
Message-ID: <20050822132441.P16438@megazone.bigpanda.com> (raw)
In-Reply-To: <EKEMKEFLOMKDDLIALABIAEKMCBAA.lvaningen@esncc.com>
References: <EKEMKEFLOMKDDLIALABIAEKMCBAA.lvaningen@esncc.com>
On Mon, 22 Aug 2005, Lane Van Ingen wrote:
> Hi, am trying to do a simple computation on two views, but for some reason
> the current_util_in computation always returns zero. All fields being used
> are integer.
>
> select a.if_id,
> a.in_count,
> a.time_incr,
> b.speed,
> ((a.time_incr * b.speed) / 8) as possible_bytes,
> (a.in_count / ((a.time_incr * b.speed) / 8) * 100) AS current_util_in,
> from if_history_view1 a, speed_history_view1 b
> where a.if_id = b.if_id
> and a.if_id = 2;
>
> The inner computation (a.time_incr * b.speed / 8) evaluated properly to
> 7675200.
> Add the "in_count divide operation", and the result is zero.
Integer division doesn't follow all the same rules as normal division
would. In particular (a/b)*c is not the same as a*c/b.
Also, I think you may be expecting rounding rather than truncation (and in
the case of (a.time_incr*b.speed)/8 can that not be a multiple of 8, and
if so what should happen?)
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To: pgsql-sql@postgresql.org
Cc: sszabo@megazone.bigpanda.com, lvaningen@esncc.com
Subject: Re: Why Doesn't SQL This Expression Work?
In-Reply-To: <20050822132441.P16438@megazone.bigpanda.com>
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